1. Technical Field
The present invention relates to an image processing apparatus.
2. Related Art
There are cases where an image processing apparatus color-converts image data having a grayscale value of RGB (RGB value) into image data having a grayscale value of CMYK (CMYK value) which are toner (ink) colors of a printing device for each pixel when image data is printed, and reduces the image data so as to be suitable for a printing resolution or the like.
For example, in a case where the number of pixels of the image data is reduced to ½ in the longitudinal direction, the image processing apparatus reduces two pixels adjacent in the longitudinal direction to one pixel which has a CMYK value obtained by color-converting an average value of the RGB values of the two pixels. Thereby, the image processing apparatus reduces the number of referring to a color conversion table to ½ in a case of performing a color conversion process for each pixel, and performs the image process at high speed.
However, generally, in the color conversion table, the CMYK value is not necessarily proportional to a change in the RGB value and is changed so as to draw a curve. Specifically, if a K value (black) is used as an example, in relation to a change from white (RGB=255, 255, 255) of the RGB value to black (RGB=0, 0, 0), the K value is changed so as to slightly increase from white to an intermediate color of white and black and to greatly increase around black.
In a case of being based on such a color conversion table, a CMYK value corresponding to an average value of two RGB values and an average value of CMYK values respectively corresponding to two RGB values represent different colors. For this reason, as described above, if the color conversion process is performed based on the RGB average value of the two adjacent pixels, the conversion is performed to a CMYK value which is different from an average value of CMYK values respectively corresponding to RGB values of two pixels, and this causes deterioration in image quality.
In addition, for example, JP-A-2002-16815 discloses an image processing apparatus which performs the color conversion process before and after enlargement and reduction of image data.
Therefore, the image processing apparatus acquires a CMYK value by performing the color conversion process for each pixel of image data having an RGB value, and then generates image data of a CMYK value which is reduced to ½ in the longitudinal direction by using an average value of CMYK values of two pixels in the longitudinal direction as a CMYK value of one pixel. Thereby, deterioration in image quality is prevented. On the other hand, however, there is a problem in that, since the color conversion process is performed for each pixel of image data, color conversion processes corresponding to at least the number of pixels are performed, and thus a process speed is low.